Supramolecular helical architectures dictated by folded and extended conformations of the amino acid in ternary CuII/diamine/racemic amino acid complexes

Article abstract of DOI:10.1002/ejic.200600967

The ternary Cu^II complexes [Cu(D,L-phe)(bpy)]·(ClO ₄) (1), [Cu(D,L-phe)(phen)(H₂O)]·ClO ₄·H₂O (2), and [Cu(L-phe)-(bpy)(H ₂O)]·ClO₄·H₂O (3) (bpy = 2,2′-bipyridine, phen = 1,10-phenanthroline) adopt helical structures in the crystal state, as determined by an X-ray structural analysis. The supramolecular helical assembly of these complexes was also investigated by single-crystal X-ray crystallography. The complexes derived from racemic amino acids (1 and 2) undergo spontaneous resolution in the solid state to form separate helical chains of the ternary complex that carry a single enantiomer of the amino acid. In the case of complex 1, the two helical chains resulting from the L- and D-phe complexes bear opposite chirality, which means that the bulk crystalline sample is racemic. In contrast, the two helical chains generated by L- and D-phe complexes in 2 have the same twist and pack together in a right-handed assembly. The (P)/(M) handedness of the helical chains is dictated by the conformational chirality (λ/δ) of the chelate rings of the D/L-amino acids. Wiley-VCH Verlag GmbH & Co. KGaA, 2007.

Full text of DOI:10.1002/ejic.200600967

FULL PAPER
DOI: 10.1002/ejic.200600967
Supramolecular Helical Architectures Dictated by Folded and Extended
Conformations of the Amino Acid in Ternary CuII/Diamine/Racemic Amino
Acid Complexes
Palani Sivagnana Subramanian,*[a] Eringathodi Suresh,[a] and Luigi Casella*[b]
Keywords: Helicates / Self-assembly / Copper / Chiroptical properties / Amino acids
The ternary CuII complexes [Cu(
[Cu( -phe)(phen)(H2O)]·ClO4·H2O (2), and [Cu(
D,L
-phe)(bpy)]·(ClO4) (1),
two helical chains resulting from the L- and D-phe complexes
bear opposite chirality, which means that the bulk crystalline
sample is racemic. In contrast, the two helical chains gener-
ated by L- and D-phe complexes in 2 have the same twist
and pack together in a right-handed assembly. The (P)/(M)
D,L
L-phe)-
(bpy)(H2O)]·ClO4·H2O (3) (bpy = 2,2Ј-bipyridine, phen =
1,10-phenanthroline) adopt helical structures in the crystal
state, as determined by an X-ray structural analysis. The
supramolecular helical assembly of these complexes was also
investigated by single-crystal X-ray crystallography. The
complexes derived from racemic amino acids (1 and 2) un-
dergo spontaneous resolution in the solid state to form sepa-
rate helical chains of the ternary complex that carry a single
enantiomer of the amino acid. In the case of complex 1, the
handedness of the helical chains is dictated by the conforma-
tional chirality (λ/δ) of the chelate rings of the
D/L-amino
acids.
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2007)
number of researchers, including Raymond et al.[15] and Al-
brecht et al.[16] Recent articles by Kuroda et al.,[1a,17] how-
ever, have explored the chiroptical properties exhibited by
achiral complexes. The self-assembled, single-stranded
supramolecular architecture of ternary [CuII(DA)(AA)]
complexes obtained from a simple one-pot reaction that
contain the amino acid in their helical skeleton inspired us
to investigate their optical behavior. In the structure of the
complexes [Cu(,-phe)(bpy)]·ClO4 (1), [Cu(,-phe)-
(phen)(H2O)]·ClO4·H2O (2), and [Cu(-phe)(bpy)(H2O)]·
ClO4·H2O (3) that we describe here (bpy = 2,2Ј-bipyridyl;
phen = 1,10-phenanthroline), the difference in the orienta-
tion of the phenylalanine side chain results in folded and
extended conformations of the amino acid chelate ring that
lead to noncovalently propagated supramolecular helical
architectures. Folded and extended forms of ternary aro-
matic amino acid complexes have been reported by many
researchers,[2,5,7–9] and here we show how these conforma-
tions can influence the helicity of the polymeric structure
of the ternary complexes. Complexes 1 and 2, which contain
racemic phenylalanine, undergo spontaneous resolution in
the crystalline state and their different supramolecular heli-
cal structures result in interesting differences in chiroptical
properties in the solid state. The potential sources of optical
activity in the ternary complexes 1–3 are discussed in terms
of the ∆/Λ configuration of the CuII chromophoric units,
the supramolecular helicity (P)/(M), and the λ/δ conforma-
tional chirality of the nonplanar /-amino acid chelate
rings.
Introduction
Compounds that are achiral in nature but gain chiropt-
ical properties upon formation of supramolecular helical
architectures have received a great deal of interest in recent
years.[1] A number of ternary CuII/diamine (DA) complexes
with optically active - and -amino acids (AA), where the
latter residues can be present in folded and extended con-
formations, are known, and their optical properties in solu-
tion have been studied extensively.[2–4] Many of the investi-
gations on such [CuII(DA)(AA)][5–9] complexes reported so
far have focused mainly on structure/reactivity correlations
and conformational studies; no correlation between their
structural architecture and solid-state optical properties has
been reported. Inorganic metallohelicates[10] are known to
have interesting chiroptical properties. Intensive efforts to
amplify the chiroptical properties obtained by supramolec-
ular helicity by introducing various chiral residues or mole-
cules such as chiral spacers,[11,12] amino acids,[13,14] and chi-
ragens[14] into the helical skeleton have been made by a
[a] Analytical Science Division, Central Salt and Marine Chemi-
cals Research Institute,
Gijubhai Badhegha Marg, Bhavnagar, 364002, Gujarat, India
Fax: +91-278-256-6970
E-mail: siva@csmcri.org
[b] Dipartimento di Chimica Generale, Università di Pavia,
Via Taramelli 12, 27100 Pavia, Italy
Fax: +39-0382-528-544
E-mail: bioinorg@unipv.it
Supporting information for this article is available on the
WWW under http://www.eurjic.org or from the author.
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Eur. J. Inorg. Chem. 2007, 1654–1660

Supramolecular Helical Architectures in Ternary CuII Complexes
Results and Discussion
FULL PAPER
bonds [Cu1–O4 2.274(2), Cu2–O2 2.261(2) Å] formed by
O2 and O4 of phenylalanine in 1 define a folded single-
stranded helical, cationic polymeric chain along the a axis.
The carboxylate oxygen atom O2 coordinated to Cu(2) pos-
Crystal Structures and Molecular Association
ORTEP diagrams of complexes 1–3 with the atom num- sesses an additional weak short contact with one of the two
bering schemes are given in Figure 1. A summary of the bipyridyl nitrogen atoms (O2–N4 2.910 Å) that may have
crystallographic data is given in the Experimental Section some significance for the helical arrangement. The helical
and selected bond lengths and angles for 1–3 are given in chain is constructed from –Cu1–OCO–Cu2– bonds with
Table 1. The CuII ions in complexes 1–3 possess a distorted CuII centers sitting alternatively at distances of 5.883 and
square-pyramidal geometry where the base of the square 5.864 Å. The aromatic rings of the amino acids C13 to C18
pyramid is constituted by the pyridyl nitrogen atoms of the and C32 to C37 adopt only a folded conformation in com-
heterocyclic diamines and the NH2 and CO2 groups of the plex 1 and are oriented almost parallel to the bpy rings,
amino acids (-, -phe). The fifth axial ligand is different with a slight deviation of 2.74 and 6.99°, respectively, from
and consists of a carboxylate oxygen atom in 1 and a water the mean plane, which facilitates strong intra- and intermo-
molecule in 2 and 3. The long CuII–carboxylate oxygen lecular stacking interactions (Figure 2A).
Figure 1. ORTEP diagrams of the structures of complexes 1–3.
Eur. J. Inorg. Chem. 2007, 1654–1660
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1655

P. S. Subramanian, E. Suresh, L. Casella
FULL PAPER
Table 1. Selected bond lengths [Å]and bond angles [°] for complexes (2a), Cu2–O2w 2.351 Å (2b)] in both cases, while the square
1–3.[a]
base resembles that present in complexes 1 and 3.
Similar to complex 1, the phenyl ring of -phe in 2a is
almost parallel to the phenanthroline ring (tilt angle of
5.29°) and forms a folded isomer. However, the phenyl moi-
ety of -phe in 2b is inclined towards the perpendicular of
the phenanthroline ring (tilt angle of 71.96°) to yield an
extended isomer. The folded and extended isomers 2a and
2b, respectively, in Figure 2 are packed with the phenyl ring
of the amino acid pair pointing in opposite directions and
give effective π···π stacking interactions, as shown in Fig-
ure 2D. The offset inter- and intramolecular π···π stacking
interactions between the phenyl rings of the bpy/phen li-
gands and the aromatic rings of the amino acids in com-
plexes 1 and 2 are depicted in Figure 2; the stacking dis-
tances are given in the figure caption. The weak π···π inter-
actions clearly play a significant role: the aromatic ring of
the folded phenylalanine causes the intramolecular π···π
stacking interaction and that of the extended form facili-
tates the intermolecular π···π stacking interaction, as indi-
cated by the double-headed arrows in Figure 2. Further, the
phenanthroline units of the folded and extended forms gen-
erate interhelical π···π stacking through the centroids
[Cg3(ext)···Cg2(fold) 3.539 Å] of their aromatic rings.
1
2
3
Cu1–O1
Cu1–N2
Cu1–N3
Cu1–N1
1.9432
1.9883
1.9932
1.9953
2.2742
96.0810
84.419
151.8610
177.549
81.5610
97.9910
94.588
107.939
100.059
85.529
Cu2–O3
Cu2–N6
Cu2–N4
Cu2–N5
1.9462
1.9902
1.9923
1.9953
2.2612
84.479
177.7310
97.6710
96.3010
150.9910
81.4611
94.198
103.079
86.099
105.789
Cu1–O4
Cu2–O2#1
O3–Cu2–N6
O3–Cu2–N4
N6–Cu2–N4
O3–Cu2–N5
N6–Cu2–N5
N4–Cu2–N5
O3–Cu2–O2#1
N6–Cu2–O2#1
N4–Cu2–O2#1
N5–Cu2–O2#1
O1–Cu1–N2
O1–Cu1–N3
N2–Cu1–N3
O1–Cu1–N1
N2–Cu1–N1
N3–Cu1–N1
O1–Cu1–O4
N2–Cu1–O4
N3–Cu1–O4
N1–Cu1–O4
Cu1–O1
Cu1–N3
Cu1–N2
Cu1–N1
1.952617
2.0042
2.0072
2.0102
2.2852
83.748
93.728
159.669
176.058
100.099
82.358
86.0810
100.1310
99.819
Cu2–O3
Cu2–N5
Cu2–N6
Cu2–N4
1.936417
1.9972
2.0052
2.0122
2.3512
94.488
83.088
167.9510
176.538
82.439
99.629
95.438
97.0910
94.8911
86.538
Cu1–O1w
Cu2–O2w
O1–Cu1–N3
O1–Cu1–N2
N3–Cu1–N2
O1–Cu1–N1
N3–Cu1–N1
N2–Cu1–N1
O1–Cu1–O1w
N3–Cu1–O1w
N2–Cu1–O1w
N1–Cu1–O1w
O3–Cu2–N5
O3–Cu2–N6
N5–Cu2–N6
O3–Cu2–N4
N5–Cu2–N4
N6–Cu2–N4
O3–Cu2–O2w
N5–Cu2–O2w
N6–Cu2–O2w
N4–Cu2–O2w
Supramolecular Helical Association and Chirality
The stereochemical descriptors (P) or (M) can be as-
signed to the helical assemblies in 1–3 depending on the
clockwise or anticlockwise bias of the helical strand, respec-
tively. It is noteworthy that the supramolecular packing in
complexes 1–3 generates a one-dimensional inner-sphere
helical arrangement running through the metal centers by
a combination of weak inter- and intramolecular π···π
stacking and hydrogen-bonding interactions, as shown in
Figure 2. An imaginary helical axis drawn between the
metal centers along the a axis is shown in Figure 3. In all
cases the bipyridyl ligand and the phenyl ring of the amino
acid that projects outwards revolve around the helical axis
with good intra- and intermolecular π···π stacking interac-
94.1410
Cu1–O2
Cu1–N3
Cu1–O1
O2–Cu1–N2
N2–Cu1–N3
N2–Cu1–N1
O2–Cu1–O1
N3–Cu1–O1
1.972916
1.9992
2.301414
92.068
171.508
81.087
90.736
Cu1–N2
Cu1–N1
1.980919
2.001919
O2–Cu1–N3
O2–Cu1–N1
N3–Cu1–N1
N2–Cu1–O1
N1–Cu1–O1
82.396
160.797
102.148
98.247
88.307
107.957
[a] Symmetry operation for atom #1 = x–1, y, z.
Complex 2 differs from 1 and 3 by crystallizing with two tions. The intramolecular helical structure running through
independent molecules in the asymmetric unit; one contains the Cu1–OCO–Cu2 strands in complex 1 contains only
the  isomer of the amino acid in the folded form only folded phenylalanine isomers. As expected, therefore, the
(henceforth referred to as 2a), while the other contains only arrangement of the two polymeric helical chains containing
the -amino acid in an extended form (henceforth referred the - and -amino acids in this complex occurs through
to as 2b). Similar folded and extended conformations have the formation of alternately packed (P) and (M) helices, as
already been reported in analogous ternary copper(II) com- shown in Figure 3A.
plexes such as [Cu(-trypO)(phen)]+,[18] [Cu(-phe)(phen)-
The coordinated O1w and O2w molecules of the folded
Cl]·3H2O,[8] [Cu(-o-Me-phe)(phen)(H2O)]ClO4,[5c] [Cu(- and extended conformers in complex 2 propagate the hy-
NH2Phe)(bpy)]·NO3·H2O,[8] and [Cu(-tyr)(phen)(H2O)]· drogen-bonded helical architecture through Cu1–
ClO4·1.5H2O,[8] etc. We have also recently reported a folded O1w···O2CO1–Cu1 and Cu2–O2w···O4CO3–Cu2 bonds,
conformation of -phe in the ternary complex [Cu(- respectively, diagonal to the ac plane. The O1w and O2
phe)(bpy)(H2O)]·ClO4.[9] The coordination around CuII re- (carboxylate oxygen) atoms of the adjacent molecular units
mains almost the same for both 2a and 2b, although the of the folded form are interconnected by hydrogen bonds
phenylalanine side chain varies somewhat in its orientation. (O1w···O2 2.747 Å) to form a single-stranded helical chain.
The apical coordination of the CuII square pyramid is ful- Similarly, the O2w and O4 (carboxylate oxygen) atoms
filled by long bonds with water molecules [Cu1–O1w 2.285 (O2w···O4 2.857 Å) of the extended form are interlinked
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Supramolecular Helical Architectures in Ternary CuII Complexes
FULL PAPER
Figure 2. Stacking interactions of the phenyl rings in complexes 1 and 2 along the a axis. The double-headed arrows indicate the inter-
and intramolecular stacking interactions. A: complex 1 [inter: Cg(1)···Cg(2) 4.158 Å; intra: Cg(1)···Cg(2) 4.154 Å; inter: Cg(3)···Cg(4)
4.264 Å; intra: Cg(3)···Cg(4) 4.044 Å]; B: complex 2 (only folded form); C: complex 2 (only extended form); D: merged packing of 2a
and 2b [intra: Cg(2)···Cg(6) 3.882 Å; inter: Cg(3)···Cg(2) 3.539 Å]. Color scheme: red = carboxylate oxygen; green = Cu(II).
rately in Figures 3B and C to better visualize their similar
helical chirality.
Supramolecular helices usually pack in a racemic fash-
ion,[19] and reports on homochiral helicates are rare. Supra-
molecular packing of 1, for instance, occurs with the usual
racemic pattern comprising both the (P) and (M) alternate
helical chains, while in the crystal structure of complex 2
packing of two (P) helices occurs stereospecifically to give
a homochiral superstructure, as shown in Figures 3B–D. In
complex 3, the free carboxylate oxygen atom (O2) involved
in N···H···O interactions [N(3)–H···O2 3.027 Å] forms a sin-
gle-stranded inner-sphere helical chain through the Cu1–
N3···O2CO1–Cu1 bonds along the bc plane, as shown in
Figure 3E.
Figure 3. Space-filling model of the single-stranded supramolecular
helical arrangements formed by Cu–OCO–Cu connectivity (light
gray = folded; dark gray = extended). A: 1; B: 2a, C:2b; D: addition
of both 2a and 2b; E: 3.
Chiroptical Properties
In order to understand the correlation between the
supramolecular helical architecture and the chiroptical
through hydrogen bonding to create another helical chain. properties, CD spectra for complexes 1–3 were recorded
An alternate arrangement of O–H···O interactions with the both in solution and on ground crystals. In general, the
lattice water molecule O3w and N–H···O bonds brings the optical activity could be derived from the (P)/(M) helical
adjacent folded and extended helical chains into close prox- chain chiral descriptors, the geometrical ∆/Λ descriptors of
imity to create a sheet-like architecture that restores the he- the chiral metal centers (Scheme 1), and the λ/δ conforma-
lical superstructure of the complex. The combined effect of tional chirality[20] of the nonplanar /-amino acid chelate
various O–H···O and N–H···O interactions involving O3w– rings. For systems 1–3, therefore, an attempt to correlate
O2 (2.742 Å), O3w···O2w (2.745 Å), and N(3)H···O4 their chiroptical properties can be made. Chirality at the
(3.024 Å) and π···π stacking interactions brings the CuII metal centers can be derived by taking into account the
centers into closer contact (5.928 Å). The hydrogen-bonded non-coplanar arrangement of the donor atoms at the base
helical superstructure formed by both the folded and ex- of the square pyramid in the structures of the CuII centers;
tended isomers can be designated as (P) because of the the descriptors[21] ∆ and Λ are thus assigned depending
clockwise sense of its molecular rotation, as shown in Fig- upon the clockwise (∆ isomer) and anticlockwise (Λ iso-
ure 3D. The folded and extended forms are shown sepa- mer) operation of the chromophore O(aa) Ǟ N(aa) Ǟ N(py)
Eur. J. Inorg. Chem. 2007, 1654–1660
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P. S. Subramanian, E. Suresh, L. Casella
FULL PAPER
Ǟ N(py) around the CuII center, as shown in Scheme 1. In the absolute (/) configuration of the amino acid, with a λ
complex 1, the (P) sense of the helix is associated with conformation inducing an (M) helix and a δ conformation a
∆∆∆∆... configurations at the metal centers, while the (M) (P) helix. The self-assembly process generating the helical
sense involves ΛΛΛΛ... configurations at the Cu atoms. chains is thus enantioselectively dictated by the folded or
The amino acids in complex 2 exist in folded (2a) and ex- extended disposition assumed by the side-chain of the phe
tended (2b) forms, both of which selectively assemble into residues.
(P) helical chains, although the configuration at the metal
As expected, the CD spectra of complexes 1 and 2 in
centers is Λ∆Λ∆... in the skeleton of the two helices. solution are flat as the polymeric structure is destroyed; the
Furthermore, as complexes 1 and 2 possess very similar solid-state CD spectrum of complex 1 is also essentially flat,
chemical compositions, the difference in their spatial ar- taking into account the low resolution of the experiment,
rangement caused by the folded and extended isomer and whereas crystals of complex 2 appear to exhibit optical ac-
the extra space provided by the phenanthroline ligand may tivity in the solid state, with weak but clearly detectable CD
be the reason for its homochiral nature.
activity with a positive sign between 500 and 600 nm. The
dominant CD activity for complex 3 has a negative sign
and remains unchanged both in the solid state (λmax
≈
620 nm) and in solution [CD data in methanol: λmax ≈ 565
(∆ε = –0.44 –1 cm–1) and 725 nm (+0.10)], thus clearly in-
dicating that no significant change occurs in the chiral ar-
rangement of the complex. The CD activity observed for
complexes 2 and 3 in the CuII d-d bands therefore reflects
the opposite chirality of the amino acid chelate rings and
of the corresponding helical chains associated with the two
complexes in the crystalline state.
Scheme 1. Geometrical descriptors.
As regards the conformation of the amino acid chelate
rings, it should be noted that the folded isomer has λ chiral-
ity for the -phe and δ chirality for the -phe residues, and
that the opposite chirality occurs for the corresponding ex-
tended isomers (Scheme 2). The amino acids in the helical
chains of complexes 1 and 3 adopt the folded conformation
(λ for -phe and δ for -phe), although both the folded -
phe residue in 2a and the extended -phe residue in 2b bear
the same δ chirality.
Conclusion
We have described the formation of a series of single-
stranded helical coordination polymers that contain both
covalent and hydrogen bonds as a construction element.
The two separate helical chains of the ternary complex car-
rying - and -phe residues in complex 1 bear opposite chi-
rality, which means that the crystalline sample as a whole
is racemic. In contrast, the two helical chains generated by
the - and -phe complexes in 2 have the same (P) chirality
and together form two right-handed helical assemblies. In
principle, a supramolecular arrangement involving two heli-
cal chains with (M) chirality, built from the folded () and
extended () forms of the racemic amino acid, is possible
for this complex, but is probably not observed in the crys-
talline state due to the less favorable packing. Further stud-
ies on chiral amplification to monitor the crystallization
process of metal complexes containing optically pure and
racemic amino acids are currently under way in our labora-
tory.
Scheme 2. Conformations of the amino acid chelate rings.
Experimental Section
Materials: -Phenylalanine, ,-phenylalanine, 2,2Ј-bipyridyl, and
1,10-phenanthroline were purchased from Sigma–Aldrich and used
as received. All the other reagents and solvents were commercially
available and used without further purification. Microanalysis of
the complexes was performed with a Perkin–Elmer PE 2400
series II CHNS/O elemental analyzer. FT-IR spectra for KBr pel-
lets (1% w/w) were recorded with a Schimadzu FT-COM 1 spectro-
photometer. The CD spectra were measured for KBr pellets or
methanol solutions of the complexes with a JASCO J710 dichro-
graph; a smoothing program from JASCO (version 1.53.00) was
Complex 1 assembles in alternating (P) and (M) helices
through Cu1–OCO–Cu2 chains, therefore both the contri-
butions to the overall chirality by the conformation of the
amino acid chelate rings and the configuration at the CuII
centers perfectly cancel each other out in the enantiomeric
(P) and (M) helices. In contrast, the two supramolecular
helical chains built up by the - and -phe complexes in
complex 2 bear the same (P) chirality. This shows that the
chirality of the helical chain is dictated by the conforma-
tional chirality of the amino acid chelate ring rather than used to reduce the noise of the solid-state spectra.
1658 Eur. J. Inorg. Chem. 2007, 1654–1660
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Supramolecular Helical Architectures in Ternary CuII Complexes
FULL PAPER
Table 2. Summary of the crystallographic parameters for complexes 1–3.
1
2
3
Empirical formula
Formula mass
Crystal size [mm]
Crystal description
Crystal system
Space group
a [Å]
b [Å]
c [Å]
α [°]
β [°]
C38H36Cl2Cu2N6O12
966.71
0.45ϫ0.20ϫ0.08
plates
C42H42Cl2Cu2N6O15
1068.80
0.35ϫ0.20ϫ0.10
plates
monoclinic
P21/n
13.3582(10)
25.3803(18)
14.1334(10)
90.00
113.775(10)
90
4385.1(5)
4
1.619
2192
1.170
C19H20ClCuN3O7
501.37
0.36ϫ0.26ϫ0.24
blocks
monoclinic
P21
7.2743(7)
11.3581(10)
12.5857(11)
90.00
102.845(2)
90
1013.84(16)
2
1.642
514
triclinic
¯
P1
8.3033(8)
13.7280(13)
18.2520(18)
68.282(2)
84.708(2)
82.050(2)
1912.3(3)
2
1.679
988
1.326
293(2)
22.50
γ [°]
Volume [Å3]
Z
Dcalcd. [gcm–3]
F(000)
µ (Mo-Kα) [mm–1]
Temperature [K]
2θ max
1.258
293(2)
28.27
293(2)
28.24
Observed reflections [I Ͼ 2σ(I)]
Parameters refined
Goodness of fit
Final R1 (observed data)
Final wR2 (observed data)
4930
541
1.054
0.0435
0.1263
10159
756
1.050
0.0441
3636
352
1.054
0.0222
0.1270
0.0581
Preparation of the Complexes
Supporting Information (see footnote on the first page of this arti-
cle): Table summarizing hydrogen-bonding network for complexes
1 and 2.
[Cu(
D
,
L-phe)(bpy)]·ClO4 (1):
A
mixture of ,-phenylalanine
(0.82 g, 10 mmol) and NaOH (0.20 g, 10 mmol) in distilled water
(50 mL) was added to an aqueous solution (25 mL) of
CuSO4·5H2O (1.25 g, 10 mmol) and stirred for 30 min. The solu-
tion was stirred at 50 °C for another 2 h until a pale-blue precipi-
tate had formed. An ethanolic solution (20 mL) of bipyridyl
(0.78 g) was then added dropwise and the pale-blue precipitate was
observed to dissolve to form a clear blue solution. At the end of
the reaction, NaClO4·H2O (0.7 g, 10 mmol), dissolved in distilled
water (20 mL), was added. C19H18ClCuN3O6 (483.36): calcd. C
Acknowledgments
P. S. and E. S. are grateful to Dr. P. K. Ghosh, Director of the Cen-
tral Salt and Marine Chemicals Research Institute, for his keen
interest and encouragement, and Dr. A. Granata for recording the
CD spectra.
47.30, H 3.73, N 8.71; found C 47.35, H 3.76, N 8.63. IR: ν =
˜
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[Cu(D,L-phe)(phen)(H2O)]·ClO4·H2O (2): This complex was synthe-
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[Cu(L-phe)(bpy)(H2O)]·ClO4·H2O (3): Synthesized and charac-
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Crystal Structure Determination: Data collection for 1–3 was per-
formed with a Bruker Apex CCD diffractometer using Mo-Kα radi-
ation (λ = 0.71073 Å) at 100(2) K. Absorption corrections were
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were generated with a riding model. CCDC-281899 (1), -281900
(2), and -281901 (3) contain the supplementary crystallographic
data for this paper. These data can be obtained free of charge from
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1659

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Received: October 13, 2006
Published Online: March 6, 2007
1660
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© 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2007, 1654–1660